<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style type="text/css">
        *{
            margin: 0;
            padding: 0;
            box-sizing: content-box;
        }
        body{
            display: flex;
            flex-direction: column;
            min-height: 100vh;

        }
        header,footer{
            flex:0 0 50px;
            background: #ccc;
        }
        main{
            display: flex;
            flex:1;
        }
    </style>
</head>

<body>
    <header>header.......</header>
    <main>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda</h1>
        <h1>asdasdfafda1111111111111</h1>
    </main>
    <footer>
        footer.........
    </footer>
</body>
</html>